An electronic device, such as a mobile phone and a car navigation system, has had higher performance and various functions, and often includes a light-transmissible touch panel attached onto a front surface of a display element, such as a liquid crystal display. An operator presses the touch panel with a finger or a pen while looking at the display element through the touch panel, thereby switching the functions to operate the device. This touch panel is demanded to be reliably operated and not to prevent the operator from looking at the display element.
FIGS. 4 and 5 are a side sectional view and a plane sectional view of conventional touch panel 5001 disclosed in Japanese Patent Laid-Open Publication No. 2005-11312, respectively. Upper board 501 has a film shape and is light-transmissible. Light-transmissible upper resistor layer 503 made of resistor material, such as indium tin oxide, is provided on a lower surface of upper board 501. Lower resistor layer 504 is provided on an upper surface of light-transmissible lower board 502.
Plural dot spacers made of insulating resin are arranged on an upper surface of lower resistor layer 504 by predetermined intervals. Pair of Upper electrodes are provided at both ends of upper resistor layer 503, respectively. Pair of lower electrodes 505 are provided at both ends of lower resistor layer 504 and arranged in a direction orthogonal to a direction along which the pair of upper electrodes are arranged. The upper electrodes and lower electrodes 505 are made of conductive material including silver.
Spacer 506 having a substantial frame shape is provided on an outer periphery of a lower surface of upper board 501 or on an outer periphery of an upper surface of lower board 502. An upper surface and a lower surface of spacer 506 are coated with adhesion layers causing the upper and lower surfaces of spacer 506 to adhere onto an outer periphery of upper board 501 and an outer periphery of lower board 502, respectively. Spacer 506 causes upper resistor layer 503 to face lower resistor layer 504 with a predetermined space between the layers. Spacer 506 includes cutout portion 506A to which respective end portions of the upper electrodes and lower electrodes 505 extend.
Upper wiring patterns 508 made of conductive material, such as silver, are formed on an upper surface of wiring board 507 having a film shape. Lower wiring patterns 509 made of conductive material is formed on a lower surface of wiring board 507. Insulating layers 522 covering wiring patterns 508 and 509 are formed on the upper surface and the lower surface of wiring board 507, respectively, so that both end portions of wiring patterns 508 and 509 expose from layers 522, respectively. An end of wiring board 507 is located between upper board 501 and lower board 502 in cutout portion 506A of spacer 506.
Anisotropic conductive adhesive 510 contains synthetic resin and conductive particles dispersed in the synthetic resin. Anisotropic conductive adhesive 510 causes an end of wiring board 507 to adhere onto upper board 501 and lower board 502. Anisotropic conductive adhesive 510 is conductive only in direction 5001A orthogonal to wiring board 507 and is not conductive in directions, such as directions 5001B and 5001C, in parallel with wiring board 507. Anisotropic adhesive 510 electrically connects the upper electrodes to end portions of upper wiring patterns 508 and connects lower electrodes 505 to end portions of lower wiring patterns 509.
Touch panel 5001 is located on a display surface of a display element, such as a liquid crystal display, to be attached to an electronic device. The end portions of upper wiring patterns 508 and lower wiring patterns 509 on wiring board 507 are connected to an electronic circuit of the device with a connector or by soldering.
An operator presses the upper surface of upper board 501 with a finger or a pen while looking at the display surface of the display element through the touch panel. Then, upper board 501 accordingly sags to cause upper resistor layer 503 at a pressed portion to contact lower resistor layer 504.
The electronic circuit of the electronic device alternately applies a voltage to the upper electrodes and lower electrodes 505 via upper wiring patterns 508 and lower wiring patterns 509 on wiring board 507. The electronic circuit detects the position of the pressed portion based on a voltage ratio between these electrodes, and switches functions to control the device
In conventional touch panel 5001, the end portions of upper wiring patterns 508 and lower wiring patterns 509 expose from insulating layer 522. The end portions of the upper electrodes and lower electrodes 505 positioned at region 5001D outside of spacer 506 having the substantially frame shape expose. These wiring patterns and electrodes contain silver, and hence, may be sulfurized or cause silver migration producing minute precipitates between the patterns when the wiring patterns and electrodes are used in an environment including a large amount of moisture or gas. In this case, the wiring patterns cannot be connected electrically to the electrodes stably, and prevented from having a stable insulation between the wiring patterns or between the electrodes.